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Campaign : Fall 1995 UAV IOP

Abstract

"ARESE, the ARM Enhanced Shortwave Experiment, concluded a very successful deployment to Oklahoma on November 1, 1995. The purpose of this five week long campaign was to conduct a series of instrumented flights to measure the interaction of solar energy with clear and cloudy skies to provide additional insight into recent observations of enhanced absorption in cloudy atmospheres.As such, ARESE focused on two scientific objectives:

(1) the direct measurement of the absorption of solar radiation by clear and cloudy atmospheres and the placement of bounds on these measurements; and

(2) the investigation of the possible causes of absorption in excess of the model predictions.

To accomplish these objectives, ARESE used a combination of satellite, aircraft, and ground observations to make highly accurate solar flux measurements at different altitudes throughout the atmospheric column. At the heart of this was a carefully "stacked" Twin Otter and Egrett "cloud sandwich" with the Otter at 1500 - 5000 ft and the Egrett at 43,000 ft. This was overflown by an ER-2 flying at 65,000 ft, which because of its much higher speed did not stay in constant alignment with the Twin Otter/Egrett stack but did provide periodic coincidences with these other aircraft. All three aircraft carried identical up- and down-looking "Valero" radiometers and flew over identical up-looking radiometers at the CART central and extended facilities. Radiance measurements from the GOES satellites were used to retrieve top-of-the atmosphere fluxes. These flux measurements were supplemented by a variety of cloud property measurements from the ground, the Egrett and the ER-2, including radar, lidar and multispectral measurements.

These baseline ARESE flights were conducted at the CART site from September 25 through November 1. During that time we flew twelve scientific data flights and accumulated approximately 60 hours of in-flight data under a variety of atmospheric conditions ranging from clear to solid overcast. These flights are detailed in the table below and include: cloud forcing experiments under scattered, broken, and solid overcast conditions including low, mid-, and high-level cloud decks; clear sky column absorption and surface albedo measurements; clear sky flux profiling measurements; and in-flight, co- altitude intercomparisons of flux measurements made from the two aircraft. The data appear to be of excellent quality and comprise a unique data set for testing our understanding of the absorption of solar radiation in both clear and cloudy atmospheres.

In addition to these baseline solar absorption experiments, the ER-2 also performed some key calibration experiments. These used highly accurate spectral radiance measurements from the MODIS Airborne Simulator (MAS) to calibrate radiance measurements from the GOES satellite and to improve retrieval algorithms for converting spectral radiances to spectral fluxes.

The success of this deployment was the result of the tremendous efforts of a multi-laboratory multiagency team comprised of five DOE Laboratories, three NASA Centers, about a dozen universities and three aircraft companies. The ARM Program sponsored the ground-based measurements, ARM-UAV (Unmanned Aerospace Vehicle) the coordinated Egrett and Otter measurements, and ARM and NASA the ER-2 flights. Funding was provided through the DOE's ARM Program and through DoD's Strategic Environmental Research and Development Program (SERDP).